This invention relates to voice distribution and switching and, in particular, to combining voice distribution and switching with video distribution on a broadband coaxial cable network.
Video distribution systems are known wherein video signals are distributed over a broadband coaxial network to a large number of subscribers. Further, there are also known video/voice distribution systems in which a broadband coaxial network is used to provide voice distribution concurrent with video distribution.
Video/voice distribution systems are particularly advantageous in locations where broadband coaxial networks have already been installed for video distribution, but which lack independent voice distribution networks. In these locations, the cost associated with installing and maintaining an independent voice network can be eliminated by also utilizing the broadband coaxial network for voice distribution. Further, for locations which currently support voice distribution on an independent voice network, it may be desirable to add a voice distribution system to the existing coaxial video distribution system to reduce the voice traffic on the existing voice distribution network and/or to provide a redundant path for voice communications.
One example of a known video/voice distribution system utilizing a broadband coaxial network is a system proposed by First Pacific Networks (FPN). In the FPN system, corresponding broadband RF channels (typically, 6 MHz wide) serve as upstream and downstream highways for an associated group of voice channels. To avoid interference, these corresponding RF channels are offset or shifted in frequency by a fixed amount, e.g., 192.25 Mhz.
The FPN system, however, lacks any centralized control. Therefore, each voice channel must carry all its requisite control information. Because of this and since the FPN system uses digial as opposed to analog transmission, each voice channel is required to be approximately 180Kbits/second in capacity. Using typical 6 Mhz upstream/downstream RF channels, a maximum of about 28 voice channels can, therefore, be carried within a given upstream/downstream RF pair.
As a result of this limited voice channel capacity, the FPN system is not readily useable where large scale voice distribution is desired. Moreover, since there is no mechanism in the FPN system for permitting voice channels assigned to one RF channel pair to be able to communicate with voice channels assigned to another RF pair, increased capacity cannot be realized merely by allocating additional RF channels to voice distribution. In any case, such allocation would reduce the number of allowable video channels and provide only a limited number of additional voice channels per RF channel pair. Finally, the FPN system requires equipment at each subscriber location to process the extensive control information carried in the associated voice channel. This increases the complexity and cost of the equipment.
It is therefore a primary object of the present invention to provide an improved method and apparatus for utilizing a broadband coaxial network to provide voice distribution.
It is a further object of the present invention to provide a method and apparatus for providing voice distribution and switching among a large number of subscriber locations connected to a broadband cable network.
It is still a further object of the present invention to provide a method and apparatus for providing voice distribution and switching over a broadband cable network utilizing centralized control.
It is also an object of the present invention to provide a method and apparatus for a video/voice distribution system wherein the voice distribution is greatly improved.